This invention relates generally to drive units and more particularly to lubricant circulation within such drive units.
Many vehicles presently being manufactured, such as passenger cars and trucks, have a forward mounted engine with an associated drive train extending from the engine to the rear axle. The rear axle traditionally is equipped with a drive unit such as a differential gear assembly which is adapted to transmit power from the drive shaft to the rear axles. Several other types of drive units for transmitting power are well known in the art and are widely used in industrial applications other than in vehicles.
Problems have arisen in some heavy duty drive unit applications such as, for example, heavy duty trucks. Most heavy duty trucks presently being manufactured are adapted to be driven through a rear axle differential gear. Many of these trucks are equipped with two speed axle gearing assemblies. A common type of two speed axle assembly includes a planetary gear set which is selectively engageable with the differential gear assembly. Increasing speed and load carrying capabilities of modern vehicles have increased the stresses to which axle drive units are exposed and have created some serious lubrication problems. An adequate lubricant flow over the drive unit components lubricates and helps dissipate heat which builds up within the assembly. For example, lubricant flowing rapidly across the bearings or gears can absorb heat there from and transfer it to the housing, which often has fins or other heat dissipating devices rendering it more capable of such heat dissipation.
With the ever increasing size of drive units used in industrial and vehicle applications, as for example the aforementioned two speed heavy duty truck axle having both differential and planetary gear assemblies, adequate lubricant circulation becomes increasingly difficult. Attempts have been made to provide drive units such as these with lubricant recirculation systems. Many of these systems are designed to scoop oil or other lubricant from a reservoir within the drive unit housing and randomly distribute it through the gearing assembly. However, none of the previously known systems has proved to be entirely adequate.
Centrifugal force exerted upon the lubricant by the rotating gears has caused a major problem in previously known lubrication systems. It should be noted that typical truck axle assemblies are operative generally in the 2800 to 3200 r.p.m. range. Many previously known lubrication systems do not properly direct lubricant to the bearing and gear assemblies of the drive units. As a result, centrifugal force can carry lubricant to the outer portions of the lubricant enclosure without ever having performed its intended lubricating and heat dissipating function. These lubricant "spin-out" problems may result in a welding together of the non-lubricated drive unit components.